netdev - Re: [PATCH net-next 03/14] net: rtnetlink: RTM_GETSTATS: Allow filtering inside nests

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Date:   Fri, 25 Feb 2022 08:04:22 -0800
From:   Jakub Kicinski <kuba@...nel.org>
To:     Petr Machata <petrm@...dia.com>
Cc:     Ido Schimmel <idosch@...dia.com>, <netdev@...r.kernel.org>,
        <davem@...emloft.net>, <jiri@...dia.com>, <razor@...ckwall.org>,
        <roopa@...dia.com>, <dsahern@...il.com>, <andrew@...n.ch>,
        <mlxsw@...dia.com>
Subject: Re: [PATCH net-next 03/14] net: rtnetlink: RTM_GETSTATS: Allow
 filtering inside nests

On Fri, 25 Feb 2022 09:22:19 +0100 Petr Machata wrote:
> > Why use bitfield if we only use the .value, a u32 would do?  
> 
> The bitfield validates the mask as well, thereby making sure that
> userspace and the kernel are in sync WRT which bits are meaningful.
> 
> Specifically in case of filtering, all meaningful bits are always going
> to be the set ones. So it should be OK to just handroll the check that
> value doesn't include any bits that we don't know about, and we don't
> really need the mask.

Nothing that NLA_POLICY_MASK() can't do, right? Or do you mean that 
we can when user space requests _not_ to have a group reported?
 
> So I can redo this as u32 if you prefer.

I think that'd be better, simplest tool for the job.